This disclosure relates in general to communications and, but not by way of limitation, to satellite communication systems as well as antenna design and antenna operation to reduce interference with adjacent satellites during two way communications from mobile antennas to a target satellite.
Satellites are either in geostationary orbit (GSO) which is an orbit where the satellite is stationary relative to the surface of the earth, or in non-geostationary orbit (NGSO), traveling around the earth. A GSO satellite is in orbit approximately 35,800 km above the equator, and has a revolution around the earth that is synchronized with the earth's rotation. Therefore, the GSO satellite appears fixed in the sky to an observer on the earth's surface. GSO satellites may be placed anywhere along an arc above the earth's equator, which results in a significant number of adjacent satellites in a GSO, forming an arc of satellites across the sky in GSO that is referred to herein as the geostationary arc. One potential source of signal degradation in two-way communications between antennas and a target satellite is interference to and from a satellite that is adjacent to the target satellite.
There are a number of antenna solutions suitable for two-way mobile use, e.g. on aircraft, trains, boats, or trucks. These can be classified into various categories. One category is two-axis mechanically steerable asymmetric-aperture antennas. These work well at middle and high latitude due to the low scan loss for the antenna elevation angles at these latitudes. At low latitudes, however, there are scan loss and skew issues that create interference with adjacent satellites on the geostationary arc. A second category is planar arrays. These work well at middle to low latitudes. At high latitudes, however, these antennas suffer scan loss. Therefore, neither of the two types of antennas mentioned here work well at both extremes.
In the appended figures, similar components and/or features may have the same reference label. Further, various components of the same type may be distinguished by following the reference label by a dash and a second label or a letter label in conjunction with a number label that distinguishes among the similar components. If only the first reference label is used in the specification, the description is applicable to any one of the similar components having the same first reference label irrespective of the second reference label or letter associated with the first reverence label.